The following script is for monitoring if an IP address is reachable or not. If it becomes unavailable the script will turn on a LED that is plugged into one of the GPIO pins of the Raspberry Pi. View pinout here

If you just need to assign a static IP address, to the device, because it is going to be setup as a hotspot or something, you can get away with the following.

interface wlan0
static ip_address=192.168.42.1/24

If you run into issues with it not assigning the address, check the /etc/network/interfaces file and make sure that the line that starts with “iface wlan0” says manual at the end and not static. If it says “iface wlan0 inet static”, change it to “iface wlan0 inet manual”